1. Field of the Invention
The present invention is directed toward the field of hard disk drives, and more particularly to reducing noise coupling into head-disk assemblies.
2. Art Background
One objective in designing hard disk drive storage devices is to achieve high capacity for data storage (i.e., maximizing the amount of data stored on a given amount of disk space). Storing data in a high capacity on a hard disk drive requires high-linear densities on the magnetic media, which in turn requires high recording data rates. Magnetoresistive heads, which include low inductance read and write elements, are utilized in hard disk drives to achieve high data rates. The high data rates used to achieve high recording densities also require the use of higher digital clocking rates in the control circuit of the hard disk drive. These high recording densities result in broader read channel bandwidths to read data from the magnetic media (i.e., the faster the data rate the larger the read channel bandwidth). To accommodate fast control circuit clock rates, the clock rise and fall times are minimized. Because of these factors, electromagnetic noise spectrums from the control circuit have become more broadband and more energy.
The electromagnetic noise from the control circuit can be within the large read channel bandwidth, and thus interferes with the read channel. Typically, the signal voltage levels output from the magnetoresistive heads are very small (e.g., in the hundreds of micro volts range). A head preamplifier is typically used to amplify the small output voltage levels generated from the magnetoresistive heads. The rich electromagnetic noise spectrum generated from the control circuits is easily coupled into the input stage of the head preamplifier, particularly when the head preamplifier operates to amplify data in a broad read channel bandwidth.
One prior art technique to remove electromagnetic noise involves limiting the channel bandwidth so that the frequency of most of the undesirable noise is not within the channel bandwidth. However, as discussed above, to achieve high recording densities, and consequently high storage capacities, a broader channel bandwidth is required. Therefore, reducing the channel bandwidth is an unacceptable alternative for high density hard disk drive devices. Thus, it is desirable to reduce electromagnetic noise coupled into the input stage of a head preamplifier to maximize read signal quality and overall system performance of the hard disk drive.
FIG. 1a is a top view of a prior art head-disk assembly, and FIG. 1b is a side view of a prior art head-disk assembly. An arm or actuator 120 includes magnetoresistive heads 125 that readwrite data on magnetic disk media 110. A preamplifier 130 is mounted on the actuator 120 in close proximity to the heads 125 in an attempt to reduce noise coupling at the preamplifier 130. Typically, the preamplifier 130 is grounded to the metal of the actuator 120 through a grounding screw 132. A control circuit, typically mounted on a printed circuit board (PCB) 140, is coupled to the actuator 120 via conductors 135. One of the conductors 135 is a ground connection, and the ground connection is further electrically coupled to the metal of the hard disk drive device (e.g., the base plate). Conductors 135 electrically couple the printed circuit board (PCB) 140 to the preamplifier 130 on the actuator 120. The head-disk assembly 100 configuration shown in FIG. 1a and 1b results in the coupling of noise onto the leads of the preamplifier 130 primarily through the conductors 135. For high recording density applications, this noise coupling is introduced into the read channel, thereby degrading hard disk drive performance, and inhibiting the ability to achieve high storage capacities.
As is described fully below, the present invention provides a uniform method and apparatus for noise reduction based on a complete understanding of the noise coupling mechanisms in a head-disk assembly.